Conventionally, a SiC semiconductor device made of a SiC single crystal is expected to serve as alternative device to a Si semiconductor device for a next generation power device. In order to manufacture a SiC power device with a high performance, it is required to reduce leakage current generated in SiC semiconductor and to restrict reduction of breakdown voltage of the SiC semiconductor. The leakage current and the reduction of the breakdown voltage of the SiC semiconductor are caused by defects, such as dislocations, generated in a SiC single crystal.
A sublimation recrystallization method is known as one of methods of growing a SiC single crystal. In the sublimation recrystallization method, for example, a seed crystal is joined to a pedestal disposed in a crucible made of graphite, and SiC source powder is disposed at a bottom of the crucible. Then, the SiC source powder is heated and sublimated, and sublimation gas is supplied to a growth surface of the seed crystal. Accordingly, a SiC single crystal grows on the growth surface of the seed crystal.
In the sublimation recrystallization method, if a threading dislocation that reaches the growth surface of the seed crystal exists, the SiC single crystal grows while inheriting the threading dislocation, and the threading dislocation is not reduced.
In order to solve the above-described issue, for example, JP-A-2002-121099, JP-A-2006-052097, and U.S. Pat. No. 7,501,022 disclose methods in which a seed crystal having a groove on a growth surface of the (0001) plane is used, and a SiC single crystal is grown on the growth surface of the seed crystal in the <0001> direction. In the groove on the growth surface of the seed crystal, depositing probability of atoms that contribute a crystal growth is higher in a direction perpendicular to the <0001> direction than in the <0001> direction that is a growth direction. Thus, the groove is filled with the SiC single crystal grown in the direction perpendicular to the <0001> direction, and thereby a threading dislocation is less likely to grow in the SiC single crystal. As the groove provided on the growth surface, for example, JP-A-2006-052097 discloses a groove having a wall perpendicular to the growth surface and a groove having a wall inclined from the growth surface.
However, in the above-described methods, in a case where the groove has a low aspect ratio, that is, in a case where the groove is wide and shallow, a growth ratio from a sidewall of the groove is small. Thus, a SiC single crystal does not sufficiently grow on a plane inclined from the (0001) plane, and a SiC single crystal may grow in the <0001> direction from a bottom of the groove. In the above-described case, a threading dislocation may grow in the SiC single crystal that grows from the bottom of the groove. In contrast, in a case where groove has a high aspect ratio, that is, in a case where the groove is narrow and deep, an opening portion of the groove is filled when the SiC single crystal grows, and a hollow portion may be provided in the SiC single crystal. In the above-described case, stress may be caused due to the hollow portion, and new defects may be generated.
JP-A-2006-052097 discloses that generation of a hollow portion can be restricted when an aspect ratio (i.e., depth/width) of a groove is within a range from 0.1 to 3. However, it is difficult to form such a groove with high accuracy, and a manufacturing process may be complicated.
Furthermore, in the manufacturing method using a seed crystal having a groove on a growth surface, because a crystal grows in a direction perpendicular to the <0001> direction, that is, from a pair of sidewalls opposite to each other, a joint surface is formed at a center portion of the groove. Thus, mismatching of lattice plane may be caused, for example, by thermal distortion, and a new defect may be generated in the joint surface.
The above-described issue may be caused not only in a case where a SiC single crystal is grown on a seed crystal by a sublimation recrystallization method but also in a gas supply method in which a SiC single crystal is grown in a seed crystal by introducing source gas into a crucible.